1,240 articles
Agenesis of the corpus callosum
Agenesis of the corpus callosum (AgCC, ACC): congenital absence or partial absence of the brain's interhemispheric fiber bundle, occurring in about 1:4,000 births, diagnosed by imaging, mostly of unknown cause, with variable cognitive outcomes.
Aging brain
Aging brain: age-related structural, cellular, and cognitive changes in the brain, distinguished from dementia; covers cognitive reserve, brain-age imaging, and exercise, training, and lifestyle intervention evidence.
Allergic conjunctivitis
Allergic conjunctivitis, also called ocular allergy (SAC, PAC, VKC, AKC, GPC), is IgE-mediated mast-cell inflammation of the conjunctiva causing itchy, watery, red eyes; treated stepwise with avoidance, dual-action antihistamine drops, and immunotherapy.
Alpha motor neuron
Alpha motor neuron (α-motoneuron): large lower motor neuron of the spinal cord and brainstem that innervates extrafusal muscle fibers via acetylcholine, forms motor units, follows the size principle, and degenerates in ALS.
Alpha wave
Alpha wave (alpha rhythm, Berger rhythm): 8–13 Hz EEG oscillation over posterior scalp during relaxed eyes-closed wakefulness, discovered by Hans Berger in 1924, blocked by eye opening and attention, interpreted as pulsed functional inhibition.
Alpha-synuclein
Alpha-synuclein (α-synuclein, SNCA gene product) is a 140-residue presynaptic protein; misfolded β-sheet aggregates form Lewy bodies in Parkinson's disease, dementia with Lewy bodies, and MSA, and seed amplification assays detect it diagnostically.
ALS
ALS (amyotrophic lateral sclerosis, Lou Gehrig's disease) is a fatal motor neuron disease causing progressive paralysis; most die within 3-5 years of symptom onset; riluzole, edaravone, and tofersen are approved treatments.
ALS Functional Rating Scale - Revised
ALSFRS-R (ALS Functional Rating Scale-Revised), 12-item 0-48 ordinal scale for ALS disability across bulbar, fine motor, gross motor, and respiratory domains; 1999 Cedarbaum revision, standard clinical trial primary outcome.
ALS study (NCT00821132)
NCT00821132, "Genetics of Familial and Sporadic ALS," is a Northwestern University observational genetic study led by Teepu Siddique, running 1991 to 2023 with 13,521 enrollees, collecting blood, CSF, and tissue samples from ALS families to identify ALS risk genes.
ALS–frontotemporal spectrum
The ALS–frontotemporal spectrum is a continuum of neurodegenerative disease in which amyotrophic lateral sclerosis and frontotemporal dementia overlap, sharing TDP-43 pathology and C9orf72 genetics, formally termed ALS-FTSD.
Altered level of consciousness
Altered level of consciousness (ALOC), also called altered mental status, is decreased responsiveness to external stimuli, ranging from lethargy and confusion through stupor to coma, and accounts for up to 10% of emergency department complaints.
Alzheimer's disease
Alzheimer's disease, a progressive neurodegenerative disorder defined by amyloid-beta plaques and tau tangles, is the most common dementia (60–80% of cases). Covers 2024 biological diagnostic criteria, p-tau217 blood tests, lecanemab and donanemab, ARIA risks, epidemiology, and contested amyloid hypothesis.
Amacrine cell
Amacrine cell: inhibitory retinal interneuron of the inner nuclear/ganglion cell layers, GABAergic or glycinergic, with 40–60+ types; key to direction selectivity, rod (AII) circuits, and conserved across 24 vertebrate species.
Ambidexterity
Ambidexterity: equal skill or no preference between both hands, distinct from mixed-handedness. Rare in humans (about 2% of adults); linked to weak lateralization, negligible cognitive differences, and no confirmed corpus callosum enlargement.
Amblyopia
Amblyopia, or lazy eye, is childhood vision loss from abnormal brain-eye development, with refractive, strabismic, and deprivational types; treated by patching, atropine, and newer binocular therapies.
American Academy of Neurology
American Academy of Neurology (AAN), professional society of neurologists founded 1948 by A.B. Baker, headquartered in Minneapolis; 40,000+ members, publishes Neurology and Continuum, sets expert-witness and conduct standards, and advocates for brain health.
Amoebic keratitis
Amoebic keratitis, also called Acanthamoeba keratitis (AK), is a rare, severe corneal infection caused by free-living amoebae, mainly Acanthamoeba, marked by pain out of proportion to findings, ring infiltrates, contact lens and water exposure, and months of biguanide-diamidine therapy.
Amsler grid
Amsler grid: self-test chart of straight lines with a central dot, devised by Marc Amsler and marketed from 1947, used daily by AMD patients to detect metamorphopsia and central scotomas; high specificity, moderate sensitivity.
Amygdala
Amygdala: group of nuclei in the anterior medial temporal lobe central to fear conditioning, emotion recognition, and memory modulation; key divisions are the basolateral complex, central nucleus, and medial amygdala; landmark evidence from patient S.M. with Urbach-Wiethe disease.
Amygdala hijack
Amygdala hijack, also called emotional hijack, is Daniel Goleman's 1995 term for a sudden emotional takeover of rational thought by the amygdala; modern neuroscience rejects the fear-center mechanism it assumes.
Amyloid beta
Amyloid beta (Aβ, beta-amyloid) is a 36-43 amino acid peptide cleaved from APP by β- and γ-secretases; the main plaque component in Alzheimer's disease, a proposed innate immune antimicrobial peptide, and the target of lecanemab and donanemab.
Amyotrophic lateral sclerosis type 4
Amyotrophic lateral sclerosis type 4, or ALS4, is a rare inherited motor neuron disease caused by SETX mutations, beginning before age 25 and allowing a normal life span.
Anaesthesia of cornea
Anaesthesia of cornea (ICD-11 9A78.6, 角膜の知覚消失), loss of corneal sensation from trigeminal or corneal nerve damage; causes include herpetic keratitis, surgery, drugs, diabetes; leads to neurotrophic keratopathy.
Angiocentric glioma
Angiocentric glioma is a rare WHO grade 1 pediatric-type diffuse low-grade glioma of cortex or brainstem causing refractory seizures, defined by MYB::QKI fusion and cured by resection.
Anisocoria
Anisocoria, unequal pupil sizes, is a common sign ranging from benign physiologic anisocoria (up to 20% of people, ≤1 mm) to Horner syndrome, Adie pupil, third nerve palsy, and pharmacologic causes, evaluated by light/dark comparison and drug tests.
Ankle jerk reflex
Ankle jerk reflex (Achilles tendon reflex, ankle reflex): S1 deep tendon reflex producing triceps surae contraction and plantar flexion; tested by dorsiflexion and tendon tap, lost in S1 radiculopathy and diabetic neuropathy.
Anomalies of pupillary function
Anomalies of pupillary function (ICD-11 LA11.62; pupillary disorder, anomaly of pupil function) is a group of conditions in which iris muscles fail to regulate light entering the eye, covering miosis, mydriasis, hippus, iridoplegia, and myotonic pupil.
Anoxic-ischaemic encephalopathy
Anoxic-ischaemic encephalopathy (ICD-11 8B24.0), also called hypoxic-ischemic encephalopathy, is brain injury from combined cerebral hypoxia and ischemia, occurring after adult cardiac arrest and neonatal asphyxia, treated with cooling in newborns.
Anterior horn motor neuron
Anterior horn motor neuron (anterior horn cell, ventral horn motor neuron): a lower motor neuron of the spinal cord's anterior horn, in Rexed lamina IX, with alpha and gamma types, that innervates skeletal muscle via acetylcholine at the neuromuscular junction as the final common pathway; targeted in ALS, SMA, and polio.
Aphakia
Aphakia is the absence of the crystalline lens in the eye. This condition severely blurs vision and loses accommodation, requiring correction with an IOL or spectacles.